A typical telescopic sight for use with a firearm includes a reticle having centrally located cross hairs, i.e., a vertical centerline and a horizontal centerline. For the most part, telescopic sights include adjustment controls enabling the operator of the firearm to make several main adjustments to the telescopic sight relative to firearm. Three of these adjustments are an elevation adjustment of the horizontal hairline, i.e., movement of the horizontal hairline up or down, a lateral adjustment of the vertical hairline, i.e., left or right, and a rotational adjustment of the entire telescopic sight about the central axis of the telescopic sight.
The elevation adjustment is used to compensate for the arched path a fired projectile (bullet) will inherently follow from the muzzle of the firearm to the target. Once the elevation of a sight is properly adjusted for a given range, the intersection of the cross-hairs of the reticle will indicate a theoretical point of impact of the bullet at that range, even though the line of fire to the target, that is the actual path of the bullet, will not align with the line of sight (the straight line extension of the central axis of the telescopic sight to the target).
The lateral adjustment is used primarily for initial sighting, and also to compensate for any expected drift (left or right) by the bullet from the line of fire caused by cross winds between the firearm and the target.
The process of making elevation and windage adjustments to the sight of a firearm is called "sighting in". Typically, both adjustments never remain consistent and are often difficult to adjust accurately prior to test-firing the firearm.
Apart from collimating the sight with the firearm, the mounted telescopic sight is rotatable about its central axis to adjust the relative position of the cross hairs of the sight with respect to the longitudinal and vertical axis of the barrel of the firearm. The adjustment is made to ensure that the vertical cross hair of the sight coincides with the vertical axis of the firearm. This adjustment may be easy made using a padded vice or cradle and a machinist's level and a known vertical reference line. However, in the field, this adjustment has been proven to be quite difficult to execute accurately due to the lack of a known vertical reference line with respect to the bore axis of the barrel of the firearm.
One common method used to attempt to align the vertical cross hair of the sight with respect to the bore axis of the firearm includes holding the firearm perfectly level with respect to the ground and then "sighting in" on a reference line, such as the edge of a building or a telephone pole which is known vertical with respect to the ground. With this method, the telescopic sight is simply rotated until the reference line and the vertical cross hair align. Unfortunately, however, this method is rarely successful because without the previously mentioned machinist's level and padded vise there is no indication of when the firearm is being held truly level with respect to the ground. Since it is common to hold a firearm, such as a rifle, at a slight tilt or cant, any adjustment to the reticle will reflect the angle of the cant and will invariably fail to be truly aligned with the bore axis of the barrel of the firearm.
The problem with aligning the vertical hairline with respect to the bore axis of the firearm is that there is no fixed reference line against which such an adjustment may be accurately and easily made. Conventional mounts for mounting a sight to a firearm do not restrict or otherwise provide "self-alignment" of the mounted sight with respect to the bore axis of the firearm. Any reference line located on the sight will not remain (or may never be) consistently aligned with respect to the bore axis of the firearm, and therefore may not be used to properly adjust the hairlines of the reticle with respect to the bore axis of the firearm.
Devices are commercially available to enable the user of a firearm to collimate the mounted sight of the firearm for a given target range and windage, prior to the firing of any bullets. U.S. Pat. Nos. 3,908,282, 3,744,133, 3,112,567 and 4,095,347 disclose collimators for aiding in the proper adjustment of a telescopic sight mounted to a firearm, and include an alignment reticle and a weight which are together pivotally connected to a bore mount. During collimation, the devices of the above-listed prior art references are attached to the firearm within the bore of the barrel allowing gravity to draw the weight downward and the opposing alignment reticle upward, above the barrel of the firearm and into the line of sight. All the necessary adjustments to the sight may be made by visually "sighting in" the cross-hairs of the sight against the alignment reticle. Unfortunately, the rotation adjustment of the reticle of the sight may not be accurately made using the prior art devices of the above-listed references because the alignment reticle is aligned only with respect to gravity and not the bore axis of the firearm. During collimation, the firearm may be easily held in a canted position, in which case the cross-hairs of the reticle of the sight would be misaligned with respect to the bore axis of the firearm. This misalignment between the cross-hairs of the reticle and the bore-axis of the firearm may easily result in inaccurate firing and difficult re-adjustment of the scope after a test firing.
A reticle alignment device is available from the B-Square Company of Fort Worth, Texas, which comprises a bent piece of clear plastic which is approximately rectangular in cross section and includes a horizontal portion which is sized to roughly fit into the receiver of bolt-action rifles. Once inserted within the receiver of the rifle, the horizontal portion of the device aligns on the bolt-way flats. A vertical portion of the device, which includes a reference line, projects upward from the receiver just in front of the eyepiece of the sight. The user may align the vertical cross hair of the sight with the reference line provided by the B-Square device.
The B-Square alignment device may only be used with bolt-action type rifles having a particular arrangement of bolt-way flats and not with any other type of action (pump, auto, single shot, etc.). Even in those situations where the B-Square device may be used, it is often difficult to accurately align the fine cross hairs of the sight with the overlapping reference line of the B-Square device because the reference line interferes with the line of sight, being positioned exactly where the reference line should be. In adjusting the sight using the B-Square, the user loses sight of the vertical cross hair behind the interfering reference line when the cross hair nears the correct position but is not necessarily at the correct position.
It is, therefore, an object of the present invention to provide an easy-to-use reticle alignment device which overcomes the problems of the prior art.
Another object of the invention is to provide an easy to use device for quickly aligning the cross-hairs of the reticle of a firearm-mounted telescopic sight with respect to the bore axis of the firearm.
A still further object of the invention to provide a reticle alignment device which has not-interfering reference lines for aligning the cross-hairs of the reticle of a firearm-mounted telescopic sight with respect to the bore axis of the firearm.